Rectifying circuit with thyristors

ABSTRACT

A rectifying circuit including: between a first terminal of application of an AC voltage and a first rectified voltage delivery terminal, at least one first diode; and between a second terminal of application of the AC voltage and a second rectified voltage delivery terminal, at least one first anode-gate thyristor, the anode of the first thyristor being connected to the second rectified voltage delivery terminal; and at least one first stage for controlling the first thyristor, including: a first transistor coupling the thyristor gate to a terminal of delivery of a potential which is negative with respect to the potential of the second rectified voltage delivery terminal; and a second transistor connecting a control terminal of the first transistor to a terminal for delivering a potential which is positive with respect to the potential of the second rectified voltage delivery terminal, the anode of the first thyristor being connected to the common potential of voltages defined by said positive and negative potentials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of French patentapplication number 15/62393, filed on Dec. 15, 2015, the content ofwhich is hereby incorporated by reference in its entirety to the maximumextent allowable by law.

BACKGROUND Technical Field

The present disclosure generally relates to electronic circuits and,more specifically, to the forming of a rectifying bridge based on diodesand thyristors.

Description of the Related Art

Many implementations of controllable rectifying bridges, based on theuse of thyristors, are known.

For example, U.S. Pat. No. 6,493,245 describes a rectifying bridgehaving two cathode-gate thyristors provided in the upper portion of thebridge, that is, with the cathodes connected to the positive potentialof the rectified voltage.

BRIEF SUMMARY

An embodiment overcomes all or part of the disadvantages of usualrectifying bridges with thyristors.

Another embodiment more specifically provides a controllable rectifyingbridge having a simplified control.

Another embodiment provides a controllable rectifying bridge compatiblewith applications where the current of the load controlled by the bridgevaries by significant proportions.

Thus, an embodiment provides a rectifying circuit comprising:

-   -   between a first terminal of application of an AC voltage and a        first terminal of delivery of a rectified voltage, at least one        first diode;    -   between a second terminal of application of the AC voltage and a        second terminal of delivery of the rectified voltage, at least        one first anode-gate thyristor, the anode of the first thyristor        being connected to the second rectified voltage delivery        terminal; and    -   at least one first stage for controlling the first thyristor,        comprising:    -   a first transistor coupling the gate of the thyristor to a        terminal of delivery of a potential negative with respect to the        potential of the second terminal of delivery of the rectified        voltage; and    -   a second transistor connecting a control terminal of the first        transistor to a terminal of delivery of a potential which        positive is with respect to the potential of the second        rectified voltage delivery terminal,    -   the anode of the first thyristor being connected to the common        potential of voltages defined by said positive and negative        potentials.

According to an embodiment, the circuit further comprises:

-   -   between the second terminal of application of the AC voltage and        the first terminal of delivery of the rectified voltage, at        least one second diode;    -   between the first terminal of application of the AC voltage and        the second terminal of delivery of the rectified voltage, at        least one second anode-gate thyristor, the anode of the second        thyristor being connected to the second terminal of delivery of        the rectified voltage; and    -   at least one second stage for controlling the second thyristor,        comprising:    -   a third transistor coupling the gate of the second thyristor to        said terminal of delivery of said negative potential; and    -   a fourth transistor connecting a control terminal of the third        transistor to said terminal of delivery of said positive        potential.

An embodiment provides a rectifying circuit comprising:

-   -   a first terminal and a second terminal, intended to receive an        AC voltage;    -   a third terminal and a fourth terminal, intended to deliver a        rectified voltage;    -   a rectifying bridge having input terminals respectively        connected to the first and second terminals, and having    -   output terminals respectively connected to the third terminal,        and connected by a first anode-gate thyristor to the fourth        terminal; and    -   a stage for controlling the thyristor comprising:    -   a first transistor coupling the gate of the first thyristor to a        terminal of delivery of a potential which is negative with        respect to the potential of the second terminal of delivery of        the rectified voltage; and    -   a second transistor connecting a control terminal of the first        transistor to a terminal of delivery of a potential which is        positive with respect to the potential of the second rectified        voltage delivery terminal,    -   the anode of the first thyristor being connected to the common        potential of voltages defined by said positive and negative        potentials.

According to an embodiment, the second or the second and fourthtransistors are controlled by a digital circuit.

According to an embodiment, a resistive element is interposed betweenthe gate of the first or of each thyristor and the first transistor oreach of the first and third transistors.

According to an embodiment, a resistive element is interposed betweenthe base of the first or of each of the first and third transistors andthe second or each of the second and fourth MOS transistors.

According to an embodiment, the first or the first and third transistorsare bipolar transistors, preferably of NPN type.

According to an embodiment, the second or the second and fourthtransistors are MOS transistors.

According to an embodiment, the control circuit is powered with apositive voltage delivered by a power supply circuit connected to thefirst rectified voltage delivery terminal, a capacitor connecting thepower supply circuit to the second rectified voltage delivery terminal.

According to an embodiment, said negative potential is obtained, fromthe power supply circuit, by a charge pump circuit.

According to an embodiment, at least one diode series-connected with aresistive element connects the second terminal of delivery of therectified voltage to one of the terminals of application of the ACvoltage.

The foregoing and other features and advantages will be discussed indetail in the following non-limiting description of specific embodimentsin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an electric diagram of an example of a known rectifying bridgewith thyristors;

FIG. 2 is a block diagram of an embodiment of a controllable rectifyingcircuit with thyristors;

FIG. 3 is an electric diagram of an embodiment of the circuit of FIG. 2;

FIG. 4 illustrates an example of a circuit for generating a negativevoltage for the rectifying bridge of FIGS. 2 and 3;

FIG. 5 illustrates a starting circuit for the controllably rectifyingcircuit shown in FIGS. 2 and 3;

FIG. 6 is an electric diagram illustrating an alternative embodiment ofa starting circuit; and

FIG. 7 is a block diagram illustrating a controllable rectifying circuitutilizing diodes.

DETAILED DESCRIPTION

The same elements have been designated with the same reference numeralsin the different drawings. For clarity, only those steps and elementswhich are useful to the understanding of the described embodiments havebeen shown and will be detailed. In particular, what use is made of therectified voltage has not been detailed, the described embodiments beingcompatible with usual applications of such a rectified voltage. Further,the circuits for generating control signals from a microcontroller havenot been detailed either, the described embodiments being here againcompatible with usual control signal generation circuits. Forsimplification, in the following explanations, forward voltage dropswill be neglected in the diodes and the thyristors.

FIG. 1 is an electric diagram of an example of a controllable rectifyingbridge with thyristors of the type described in above-mentioned documentU.S. Pat. No. 6,493,245. This bridge is a fullwave bridge and comprisestwo parallel branches between two terminals 11 and 12 of delivery of arectified voltage Vout. Each branch comprises a thyristor Th1,respectively Th2, connected to a diode D1, respectively D2, the diodeanodes being on the side of terminal 12 which defines the most negativepotential (generally the ground or reference potential) of rectifiedvoltage Vout. The respective junction points of the thyristors and ofthe diodes define two terminals 13 and 14 of application of an ACvoltage Vac to be rectified. A capacitive element C is generallyconnected between terminals 11 and 12 to smooth the rectified voltage.

Thyristors Th1 and Th2 are cathode-gate thyristors intended to becontrolled from a signal CT.

In such a controllable rectifying bridge, a control voltage directlyoriginating from a microcontroller cannot be applied, neither can, moregenerally, a voltage directly referenced to reference potential 12, dueto the reference of the cathodes of thyristors Th1 and Th2, which is onthe side of the most positive potential (terminal 11) of the rectifiedvoltage. This imposes using a conversion element 15 of galvanicisolation transformer or optocoupler type to convert the reference ofthe control signal.

Such an embodiment increases the production costs of a controllablerectifying bridge.

FIG. 2 schematically shows in the form of blocks an embodiment of acontrollable rectifying circuit (rectifying bridge with thyristors).This circuit comprises a rectifying bridge having two parallel branchesbetween two terminals 21 and 22 of delivery of a rectified voltage Vout,terminal 22 representing a reference potential, such as ground GND. Eachbranch comprises a diode D3, respectively D4, connected to a thyristorTH3, respectively TH4, between terminals 21 and 22, the thyristorshaving anodes connected to terminal 22 and the diode cathodes beingconnected to terminal 21. The respective midpoints of the two branchesdefine terminals 23 and 24 of application of an AC voltage Vac to berectified, terminal 23 being connected to the anode of diode D3 and tothe cathode of thyristor TH3, terminal 24 being connected to the anodeof diode D4 and to the cathode of thyristor TH4. A filtering capacitiveelement C is preferably connected between terminals 21 and 22.

Thyristors TH3 and TH4 are anode-gate thyristors. The respective gatesof thyristors TH3 and TH4 receive control signals from a control circuit3 of digital control circuit or microcontroller type (CTRL), via controlstages 4 and 5. Control circuit 3 is for example a microcontroller or anintegrated circuit powered from a low positive voltage (for example,having a value in the range from 3.3 volts to 12 volts). Low positivevoltage Vdd is provided between a terminal 25 at a positive potentialVdd and terminal 22. Voltage Vdd is low as compared with voltage Vout(in the range from some ten volts to several hundreds of volts).

For a current to flow in one of thyristors TH3 and TH4, the anodevoltage should be greater than the cathode voltage and it should beactivated by the drawing of a current onto its gate. Since the anodes ofthyristors TH3 and TH4 are connected to terminal 22, to draw a currentonto their respective gates, the latter have to be taken to a negativepotential with respect to ground. To be able to directly process (withno optocoupler or the like) the control signals received from controlcircuit 3, control stages 4 and 5 are powered from positive potentialVdd (terminal 25). However, to be able to take the gates to a negativepotential, the reference (low potential) of control stages 4 and 5,instead of being the ground, is a negative potential −Vdd′ provided on aterminal 26. The absolute values of potential Vdd and −Vdd′ may beidentical or different according to the positive and negative voltagesadapted to the application and to the components and circuits used.

FIG. 3 is an electric diagram of an embodiment of the circuit of FIG. 2.FIG. 3 details, in particular, examples of the forming of control stages4 and 5 and of generation of positive voltage Vdd.

Each control stage 4, 5 comprises a resistor, respectively R4, R5, inseries with a bipolar transistor T4, T5, of type NPN, between the gateof thyristor TH3, respectively TH4, and terminal 26 at potential −Vdd,the emitter terminals of transistors T4 and T5 being connected toterminal 26. The base of transistor T4, respectively T5, is connectedvia a MOS transistor M4, respectively M5, series-connected with aresistor R4′, respectively R5′, to terminal 25 at potential Vdd.Transistor M4, respectively M5, is on the side of terminal 25. The gatesof transistors M4 and M5 are connected to outputs of control circuit 3providing DC control signals. Control circuit or microcontroller 3 may,on the other hand, receive information from other circuits, not shown.

The gates of transistors M4 and M5 are, in the quiescent state, atpotential Vdd. Thus, transistors M4 and M5 are off, as well astransistors T4 and T5. Thyristors TH3 and TH4 are then off and therectifying bridge is off.

To turn on one of thyristors TH3 or TH4, circuit 3 takes its outputconnected to the gate of the corresponding transistor M4 or M5 toground. Thus, transistor M4, respectively M5, turns on. A base currentis then injected into the base of transistor T4, respectively T5, whichturns it on. A gate current is then drawn onto the gate of the concernedthyristor TH3 or TH4 and the corresponding branch of the bridge is thuson.

In practice, thyristor TH4 is turned on during positive halfwaves ofinput voltage Vac and thyristor TH3 is turned on during negativehalfwaves.

Resistors R4′, R5′, R4, and R5 enable to set the current in therespective bases of transistors T4 and T5 and in the respective gates ofthyristors TH3 and TH4.

As a variation, MOS transistors M4 and M5 are replaced with bipolartransistors, for example, if control circuit 3 can provide a currentcontrol. Similarly, bipolar transistors T4 and T5 may be replaced withMOS transistors.

Positive voltage Vdd may originate from an external power supply sourcebut is, preferably, generated by a power supply circuit 6 (DC/DC) fromvoltage Vout. A capacitive element Ca is connected between power supplycircuit 6 and terminal 22. Power supply circuit 6 is of voltageregulator type to provide a power supply voltage adapted to controlcircuit 3.

Preferably, negative voltage −Vdd′ is obtained, indirectly from voltageVout, by a circuit 7 (NS) generating, from voltage Vdd, voltage −Vdd′.

FIG. 4 shows an example of a circuit 7 for generating a negative voltage−Vdd′.

In this example, circuit 7 has the shape of a capacitive charge pump andcomprises, between terminals 26 and 22, a first capacitor C71 and, inparallel, two series-connected diodes D72 and D73, the anode of diodeD72 being coupled to terminal 26. Junction point 74 of diodes D72 andD73 (anode of diode D73 and cathode of diode D72) is connected, by asecond capacitor C75 in series with a resistor R76, to a terminal 77 ofapplication of a train of pulses at potential Vdd. Terminal 77 is forexample connected to an output terminal of digital control circuit 3.The operation of a charge pump circuit such as illustrated in FIG. 4 isusual per se.

Other structures of generation of a negative power supply voltage may beprovided, for example with a plurality of capacitive stages.

An advantage of the described embodiments is, as compared with thecircuit of FIG. 1, that it is no longer necessary to use a conversionelement of optocoupler or galvanic insulation transformer type to applythe control signals to the thyristors. This considerably simplifies theforming of a controllable rectifying bridge and decreases the costthereof.

In an embodiment where voltages Vdd and −Vdd′ are provided by externalcircuits, the control signals may be provided by control circuit 3, evenwith an initially-discharged capacitor C.

In the embodiment of FIG. 3 where voltages Vdd and −Vdd′ are obtainedfrom voltage Vout, a starting aid should be provided.

FIG. 5 partially illustrates an embodiment of a starting circuit.

According to this example, an inductive element L is provided betweenone of terminals 23 and 24 (in FIG. 5, terminal 23) and the input of thebridge (e.g., the mid-point between diode D3 and thyristor TH3 and/orthe mid-point between diode D4 and thyristor TH4) having this terminalconnected thereto. The effect of this inductance is to slow down thegrowth of the current sampled from terminals 23 and 24 when thyristorsTH3 and TH4 are turned on while capacitor C is not charged or is onlyvery lightly charged.

Additionally or alternatively, an inductive element (not shown) may beplaced at the output, between, for example, terminal 21 and the commonpoint of the two anodes of thyristors TH3 and TH4. This inductiveelement may be placed upstream or downstream of capacitor C. This typeof element may be used, for example, in a switched power supply circuitused to correct the power factor of the current sampled from thenetwork.

FIG. 6 partially illustrates a variation of a starting circuit.

According to this example, a diode D6 connects one of the inputterminals (for example, terminal 24) to ground 22 via a resistor R6.Another diode D7 may connect the other input terminal (for example, 23)to resistor R6 to start in fullwave mode. The effect of this resistor(which generally has a temperature variation coefficient) is to enablecapacitor C to charge on powering-on, while control circuit 3 is notpowered yet and thus cannot control thyristors TH3 and TH4, which arethus in the off state (otherwise preventing any charge of C). Such anembodiment enables to power control circuit 3 while avoiding aninductive element at the bridge input.

FIG. 7 partially illustrates another embodiment where the rectifyingbridge is a fullwave bridge only formed of diodes D1, D2, D3, and D4.This amounts to replacing thyristors TH3 and TH4 with diodes D1 and D2.The bridge is then controlled by a single anode-gate thyristor THconnected between the common anodes of diodes D1 and D2 and terminal 22.Thyristor TH is controlled by a control stage circuit 4.

Various embodiments have been described. Various alterations,modifications, and improvements will occur to those skilled in the art.In particular, although the embodiments have been described in relationwith an example of a fullwave rectifying bridge, a halfwave bridge maybe provided by using a single thyristor. A multiphase network with asmany thyristor-diode arms as there are phases (for example, threethyristors and three diodes for a three-phase network) may also beprovided. Further, the generation of the control signals capable ofcontrolling the rectifying bridge depends on the application and iswithin the abilities of those skilled in the art according to thisapplication. Further, the practical implementation of the embodimentswhich have been described is within the abilities of those skilled inthe art based on the functional indications which have been describedhereabove.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A rectifying circuit, comprising: first andsecond input terminals configured to receive an AC voltage; first andsecond output terminals configured to output a rectified voltage; afirst diode coupled between the first input terminal and the firstoutput terminal; a first thyristor, the first thyristor being ananode-gate thyristor having a cathode terminal coupled to the firstinput terminal, and an anode terminal coupled to the second outputterminal; and a first control stage for controlling the first thyristor,the first control stage including: a first transistor coupling a gateterminal of the first thyristor to a negative potential supply terminalconfigured to supply a potential which is negative with respect to apotential at the second output terminal, and a second transistorcoupling a control terminal of the first transistor to a positivepotential supply terminal configured to supply a potential which ispositive with respect to the potential at the second output terminal. 2.The circuit of claim 1, further comprising: a second diode coupledbetween the second input terminal and the first output terminal; asecond thyristor, the second thyristor being an anode-gate thyristorhaving a cathode terminal coupled to the second input terminal, and ananode terminal coupled to the second output terminal; and a secondcontrol stage for controlling the second thyristor, the second controlstage including: a third transistor coupling a gate terminal of thesecond thyristor to the negative potential supply terminal, and a fourthtransistor coupling a control terminal of the third transistor to thepositive potential supply terminal.
 3. The circuit of claim 2, furthercomprising a digital control circuit, the digital control circuit beingconfigured to control at least one of the second and fourth transistors.4. The circuit of claim 2, further comprising: a first resistor coupledbetween the gate terminal of the first thyristor and the firsttransistor; and a second resistor coupled between the gate terminal ofthe second thyristor and the third transistor.
 5. The circuit of claim2, further comprising: a first resistor coupled between the controlterminal of the first transistor and the second transistor; and a secondresistor coupled between the control terminal of the third transistorand the fourth transistor.
 6. The circuit of claim 2, wherein the firstand third transistors are bipolar transistors.
 7. The circuit of claim2, wherein the second and fourth transistors are MOS transistors.
 8. Thecircuit of claim 2, further comprising: a third diode; and a resistor,the third diode and the resistor being coupled in series between thesecond output terminal and at least one of the first and second inputterminals.
 9. The circuit of claim 3, further comprising: a power supplycircuit coupled between the first output terminal and the positivepotential supply terminal, the power supply circuit being configured togenerate and provide a positive potential to the positive potentialsupply terminal; and a capacitor coupled between the positive potentialsupply terminal and the second output terminal.
 10. The circuit of claim9, further comprising: a charge pump circuit configured to generate andprovide a negative potential to the negative potential supply terminal.11. A rectifying circuit, comprising: first and second input terminals,configured to receive an AC voltage; first and second output terminals,configured to deliver a rectified voltage; a bridge rectifier circuithaving first and second bridge rectifier input terminals respectivelycoupled to the first and second input terminals, and first and secondbridge rectifier output terminals, the first bridge rectifier outputterminal being coupled to the first output terminal; an anode-gatethyristor coupled between the second bridge rectifier output terminaland the second output terminal; and a control stage for controlling thethyristor, the control stage including: a first transistor coupling agate terminal of the thyristor to a negative potential supply terminalconfigured to provide a potential which is negative with respect to apotential at the second output terminal, and a second transistorcoupling a control terminal of the first transistor to a positivepotential supply terminal configured to provide a potential which ispositive with respect to the potential at the second output terminal.12. The circuit of claim 11, further comprising a digital controlcircuit, the digital control circuit being configured to control thesecond transistor.
 13. The circuit of claim 11, further comprising: adiode; and a resistor, the diode and the resistor being coupled inseries between the second output terminal and at least one of the firstand second input terminals.
 14. The circuit of claim 12, furthercomprising a resistor coupled between the gate terminal of the thyristorand the first transistor.
 15. The circuit of claim 12, furthercomprising a resistor coupled between the control terminal of the firsttransistor and the second transistor.
 16. The circuit of claim 12,wherein the first transistor is a bipolar transistor.
 17. The circuit ofclaim 12, wherein the second transistor is a MOS transistor.
 18. Thecircuit of claim 12, further comprising: a power supply circuit coupledbetween the first output terminal and the positive potential supplyterminal, the power supply circuit being configured to generate andprovide a positive potential to the positive potential supply terminal;and a capacitor coupled between the positive potential supply terminaland the second output terminal.
 19. The circuit of claim 18, furthercomprising: a charge pump circuit configured to generate and provide anegative potential to the negative potential supply terminal.
 20. Amethod, comprising: forming a bridge rectifier circuit having first andsecond input terminals configured to receive an AC voltage, and firstand second output terminals configured to output a rectified voltage,forming the bridge rectifier circuit including: coupling a first diodebetween the first input terminal and the first output terminal, couplinga cathode terminal of a first anode-gate thyristor to the first inputterminal, and coupling an anode terminal of the first anode-gatethyristor to the second output terminal; and forming a first controlstage for controlling the first anode-gate thyristor, forming the firstcontrol stage including: coupling a gate terminal of the firstanode-gate thyristor to a negative potential supply terminal via a firsttransistor, and coupling a control terminal of the first transistor to apositive potential supply terminal via a second transistor.
 21. Themethod of claim 20, wherein forming the bridge rectifier circuit furtherincludes: coupling a second diode between the second input terminal andthe first output terminal, coupling a cathode terminal of a secondanode-gate thyristor to the second input terminal, and coupling an anodeterminal of the second anode-gate thyristor to the second outputterminal.
 22. The method of claim 21, further comprising: forming asecond control stage for controlling the second anode-gate thyristor,forming the second control stage including: coupling a gate terminal ofthe second thyristor to the negative potential supply terminal via athird transistor, and coupling a control terminal of the thirdtransistor to the positive potential supply terminal via a fourthtransistor.